The present invention relates to a single facer for the production of a single face corrugated paperboard web and, more particularly, to an auxiliary soft contact roll mounted immediately downstream of the line of joining the liner web with the glued corrugated medium web on the corrugated bonding roll to enhance the quality of the glue bond.
Recent development in single facers for the production of single face corrugated web include the elimination of a high load pressure roll for providing an initial adhesive bond and instead using a large diameter heated corrugating roll on which the single face web is retained after joinder of the component webs to provide an initial green bond in the glue lines before the single face web leaves the bonding roll. It was discovered that the relatively high impact pressure roll in a prior single facer provided an initial mechanical bond, but tended to squeeze the starch adhesive from the flute tips so that a less than satisfactory final bond resulted. Furthermore, the freshly formed single face web was removed from the corrugating roll before an adequate green bond was formed and also subjected to flexing movement which could disrupt the glue lines before an adequate bond was formed.
In an improved single facer construction, the freshly glued single face web was retained on and wrapped around a significant portion of a large diameter fluted and heated bonding roll, on which the medium web was also corrugated, so that an adequate green bond could be formed in the glue lines before the single face web was removed from the bonding roll. An apparatus of this type is shown, for example, in U.S. Pat. No. 6,149,751, the disclosure of which is incorporated by reference herein. In such an improved single facer, web tension alone was found to provide adequate force to hold the component webs together on the bonding roll while adhesive green bonds formed.
In some cases, however, it was found that the web tension by which the freshly glued single face web was wrapped on the fluted bonding roll did not provide a sufficient force to adequately hold the liner web in contact with the glued flute tips of the corrugated medium web and to spread the glue for an optimum bond. It has been found to be important to press and spread the freshly applied glue lines between the medium flute tips and the liner before gelatinization of the starch adhesive to assure uniform and optimum penetration of adhesive into the fibers of both webs. Once the adhesive has gelled, it becomes more difficult to spread and does not penetrate the paper as well. The present invention, therefore, provides an apparatus and method for enhancing the bond in a freshly glued single face web by providing an auxiliary pressure radially against the single face web on the bonding roll.